Early in human history, the wheel was discovered and human fascination with circular and spherical objects began. Humans were intrigued by devices based on these shapes: as practical transportation and propulsion, and as toys and amusements. Self-propelled spherical objects were initially powered by inertia or mechanical energy storage in devices such as coiled springs. As technology has evolved, new ways of applying and controlling these devices have been invented. Today, technology is available from robotics, high energy-density battery systems, sophisticated wireless communication links, micro sensors for magnetism, orientation and acceleration, and widely available communication devices with displays and multiple sensors for input.